Error E46

Safety precautions:

1) If you smell gas, or anyone has symptoms of carbon monoxide poisoning (headache, nausea, dizziness), leave the property and call the gas emergency number immediately. Do not attempt any checks.

2) Before doing any work on the boiler you must isolate electrical supply at the boiler isolator or consumer unit and, if you intend to work near the gas valve or gas pipework, isolate the gas supply and call a gas-safe engineer. If you are not trained, do not attempt internal electrical or gas work.

3) Wear eye protection and avoid metal tools near live circuits. If unsure, stop and call a qualified engineer.

Initial homeowner checks (non-invasive):

1) Note the exact error code and behaviour (steady code, intermittent, appears during firing or on startup). Make a note of any other codes present.

2) Try a single reset of the boiler using the reset button as per the manual. If the code returns immediately or within a short time, further investigation is needed.

3) Check that the boiler has mains power (other appliances on the same circuit working) and that the display/backlight is working. Check system water pressure is in the normal range (typically about 1–1.5 bar for many systems) because some faults appear with low pressure.

4) Visually inspect the fascia/display area for any loose knobs, signs of physical damage, moisture or corrosion around the display. Check any external cables between the fascia and the control box that are visible without removing covers.

Basic wiring and connector checks (if comfortable and the power is isolated):

1) Isolate the appliance electrical supply at the isolator and confirm the boiler is dead (display off).

2) Remove the user control knob (if applicable) and the small retaining screws for the fascia only if you are confident following the boiler manual instructions. Do not remove the outer case or touch gas components unless qualified.

3) With power isolated, gently pull the fascia forward to access the multi-pin connector (the manual mentions a 13-way connection block). Inspect the connector and cable for loose pins, bent pins, corrosion or broken wires. Reseat the connector firmly. Inspect the cable outer sheath for chafing or damage along its visible route.

4) Re-apply power and reset the boiler. If the error clears, monitor for recurrence. If intermittent, the connector/cable may be faulty and will likely need replacing by an engineer.

Checks relating to the flue/thermistor (more advanced; do not work with live gas/electrics):

1) If documentation or other sources suggest E46 can mean flue sensor open-circuit, check the flue thermistor wiring and connector at the control box (requires removing the outer case and access to internal control wiring). Isolate power first.

2) Inspect wiring and connectors for damage, water ingress or corrosion. A flue or return thermistor that is open will show infinite resistance when measured with a multimeter; a shorted sensor will show near-zero ohms. Thermistors are temperature-dependent devices and should show a measurable resistance at room temperature (if you measure open-circuit or short-circuit, the sensor is faulty). If you are not competent with electrical measurements and working inside the boiler, leave this to an engineer.

If fault persists after reseating connectors and checking sensor wiring:

1) Persistent E46 after connector/cable checks usually means either the fascia PCB or the main control box is faulty, or there is a failed sensor (flue thermistor). The service manual indicates replacement of the fascia PCB or control box as possible remedies.

2) Call a Gas Safe registered engineer or Keston-approved service technician. Provide them with the error code and detail of the checks you have already done (resetting, reseating connectors, visual inspections). The engineer can perform continuity/thermistor resistance checks, replace the fascia PCB or control box if required, and verify safe operation after repair.

Final notes and when to call a professional:

1) Any internal electrical work, replacement of PCBs, removal of the outer casing, or work near the gas valve or flue must be performed by a qualified Gas Safe engineer. Do not attempt these if you are not certified.

2) If the fault is intermittent, keep a record (times, conditions, other codes) to help the engineer diagnose. If the fault follows water ingress, corrosion, or visible cable damage, arrange a service call promptly to avoid further failures.

3) After repair, the engineer should clear the fault, confirm correct operation of the flue/sensors, and test for safe combustion and correct fan/flue temperatures per the service manual.